Underarm odor is the result of attack by microorganisms upon the excretion products of the sweat glands and sebaceous glands in the skin. There are two types of sweat glands in the underarm, i.e., eccrine and apocrine. Eccrine glands are numerous and secrete a clear aqueous sweat directly onto the skin surface, thereby serving a thermoregulatory function. The secretions of eccrine glands are not responsible for underarm odor except that they provide a warm, moist environment which encourage the growth of microorganisms. Apocrine glands, which are larger and fewer, are usually associated with sebaceous glands. The function of these glands is not understood, but their milky secretions contain nutrients for microorganisms. It is believed that the characteristic underarm odor is produced by the odorous products of microorganisms, and by the action of esterases, elaborated upon the skin by microorganisms, upon apocrine secretions
Underarm odor can be controlled in a variety of ways. Washing of the underarms controls odor only if washings are repeated throughout the day. Such repeated washing is not practicable; consequently, practically all adults in this country use a topical product to control underarm odor.
There are two classes of topical products which are effective in controlling underarm odor, i.e., antiperspirants and deodorants. Antiperspirants work by reducing the flow of eccrine perspiration to reduce wetness in the underarm area and by inhibiting the growth of microorganisms. Antiperspirant compositions are conventionally available in aerosol, roll-on and stick product forms. Clear antiperspirants typically comprise an antiperspirant active such as aluminum hydroxy chloride in a solvent, typically a lower monohydric alcohol or lower polyglycol, plus a gelling agent. Due to their acidic pH, these antiperspirant compositions inhibit microorganism growth and also chemically neutralize the odorous products formed by these microorganisms.
(Dibenzylidine sorbitol ("DBS"), a gelling agent which has been conventionally used to gel clear cosmetic compositions such as antiperspirants, is stable in alkaline neutral or slightly acidic compositions. In additions to gelling, or solidifying, topical compositions, DBS frequently imparts transparency or translucency to these compositions).
Despite their microorganism-inhibiting acidity, conventional antiperspirant compositions have been found to have numerous shortcomings. The most siw.about.yvysant shortcoming is that the antiperspirant active may irritate the skin of some users. Furthermore, when non-volatile glycols, for example, propylene glycol, are used as the solvent, the composition can impart an unpleasant stickiness to the skin. When components of the solvent are volatile, these components may evaporate during storage, leading to a drying of the composition or even to physical shrinkage in the product's size. Further, these compositions typically must include a stabilizer ingredient. Finally, high temperatures are required to solubilize dibenzylidine sorbitol as the gelling agent in certain formulations.
Deodorant compositions, also available in aerosol, roll-on and stick product forms, typically comprise an antimicrobial agent to inhibit the growth of microorganisms and a fragrance to mask odor. Conventional deodorant active ingredients include bacteriostatic quaternary ammonium compounds such as cetyl trimethyl-ammonium bromide and benzalkonium chloride, as well as zinc salts such as zinc citrate. In deodorant stick compositions, the antimicrobial agent and fragrance are carried in a low volatility solvent, such as propylene glycol, and solidified by a gelling agent such as a soap. DBS is a suitable alternative gelling agent. When DBS is so used, deodorant compositions further include an emollient such as di-n-butyl-phthalate and a polar solvent such as ethanol, as described in U.S. Pat. No. 4,816,261.
These conventional deodorant compositions have several shortcomings. The glycol and soap in these compositions create an unpleasant sticky feel on the skin. To retain their solidity, the conventional deodorant compositions must have an alkaline pH, because soap compounds are chemically stable only in alkaline formulations. Consequently, conventional deodorant compositions do not impart an acidic pH to the skin, and so are unable to exploit the benefits of an acidic composition, i.e., inhibiting microorganism growth and chemically neutralizing the odorous products of microorganisms. Further, the antimicrobial actives of several deodorants have been found to irritate the skin of a significant number of users. As with antiperspirant compositions described above, the presence of volatile solvents can lead to drying and shrinking of the solid composition upon storage. Moreover, when the gelling agent is DBS, a high heat of processing (i.e., up to 170.degree. C.) is necessary. The presence of phthalate esters as emollients in deodorant compositions solidified by DBS also requires high processing temperatures, e.g., 170.degree. C., to fully dissolve and disperse all components through the solvent. Still further, when the deodorant composition includes a phthalate ester as an emollient, there is the possibility of imparting a toxic effect to the skin from these esters. The resulting gels also are easily fractured and are opaque instead of clear. Finally, the deodorant effect from conventional deodorant compositions is short lived.
Certain esters of low molecular weight, water soluble acids such as hydroxycarboxylic acids, are known to have the ability to reduce the growth of microorganisms on the skin. Examples of such esters are glyceryl triacetate and triethyl citrate. Without in any way restricting the invention, it is believed that esterases elaborated by microorganisms on the skin hydrolyze the water-insoluble esters, when such esters are applied topically, to release water soluble acids. The resulting lowered skin pH inhibits the growth of the microorganisms and chemically neutralizes odorous products of microorganisms and of the action of bacterial esterases on apocrine secretions. The ability of microorganisms to produce underarm odor is thus reduced. Although the skin's natural buffering ability eventually neutralizes these acids and esterases again become active, the hydrolysis of the remaining esters on the skin again lowers skin pH to inactivate the esterases and prevent or delay development of unpleasant odor. Optionally, these esters of water soluble acids may be delivered to the skin with an anti-oxidant to enhance the deodorant effect, as described in Cosmetics and Toiletries, 95, July 1980, 48-50.
It would be desirable to produce a solid topical deodorant composition which produces an acid pH on the skin. Such a composition would allow one to exploit the inhibition of microorganism growth and chemical neutralyzation of odorous products which an acidic pH causes. It would additionally be desirable that this deodorant composition produce no unpleasant skin feel, not dry out, and not require the presence of co-solvents or stabilizing agents therein or the use of high processing temperatures in its manufacture. Finally, because consumers have exhibited a strong preference for clear (i.e., transparent or translucent) cosmetic compositions, including deodorant compositions, it would be desirable for this deodorant composition to be clear.